Nonlinear processes reinforce extreme Indian Ocean Dipole events

Area of Science:

• Climate Science
• Oceanography
• Atmospheric Science

Background:

• Global warming is projected to increase the frequency of extreme positive Indian Ocean Dipole (pIOD) events.
• Extreme pIOD events are linked to severe weather impacts in surrounding regions.
• The underlying mechanisms driving the projected increase in extreme pIOD events require further investigation.

Purpose of the Study:

• To analyze the heat budget of extreme pIOD events using climate models.
• To investigate the role of nonlinear heat advection in reinforcing pIOD events.
• To understand the impact of greenhouse warming on pIOD event frequency and intensity.

Main Methods:

• Analysis of 19 climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5).
• Detailed heat budget analysis focusing on nonlinear zonal and vertical heat advection.
• Examination of changes in Walker circulation and sea surface temperature anomalies (SSTAs).

Main Results:

• Nonlinear zonal and vertical heat advection are key processes reinforcing extreme pIODs.
• Greenhouse warming does not significantly alter the amplitude of these nonlinear processes.
• The frequency of extreme pIOD events increases due to a faster-warming western tropical Indian Ocean and a weaker Walker circulation.
• Smaller magnitude SSTAs are sufficient to shift convection westward, leading to more frequent extreme events.

Conclusions:

• Weakening Walker circulation under global warming causes differential ocean warming, increasing extreme pIOD event frequency.
• Positive feedback between wind, ocean currents, and heat advection intensifies moderate pIOD events into extreme ones.
• Future climate projections indicate a significant rise in extreme pIOD events with substantial regional weather implications.